A magnitude-6.5 earthquake struck off the coast of Northern California Saturday afternoon, shaking buildings, knocking out power in several coastal communities and leaving a trail of broken windows and dishes south of the Oregon border.

The powerful quake hit at about 4:27 p.m. PST about 22 miles from Ferndale, the U.S. Geological Survey said.

Authorities in the nearby city of Eureka and other area communities said no major injuries have been reported. But several people received minor cuts and scrapes from broken glass at the Bayshore Mall in Eureka, and an elderly person fell and broke a hip, authorities said.

"We're mostly getting reports of bumps, bruises and hits on the head," said Laurie Watson Stone, a spokeswoman for St. Joseph Hospital, a 146-bed hospital in Eureka. "The emergency room is busy, but we haven't heard of any major injuries."

Amanda Nichols, a dispatcher for Eureka Police Department, said she received a report that an infant was struck in the head with some flying debris at the mall.

Pacific Gas & Electric Co. spokesman J.D. Guidi said power outages were widespread across most of Humboldt County, affecting about 25,000 customers.

Nearly 10,000 remained without power some five hours after the quake, and some could remain without power through Sunday, said PG&E spokeswoman Janna Morris.

No damage was done to the company's former nuclear power plant outside Eureka, Morris said.

Several traffic lights fell and numerous residents reported water, gas and sewer leaks, Humboldt County Office of Emergency Services spokeswoman Jo Wattle said.

"People have chimneys down, and we're hearing about minor property damage and lots of glassware broken," Wattle said. "People are really shaken up. It was shaking pretty good, then it had a big jolt to it at the end."

According to the USGS, the quake hit at a depth of nearly 10 miles. At least nine aftershocks of magnitude-3.0 or above followed in the hours after the quake, the biggest registering at 6:21 p.m. PST at a magnitude of 4.5.

Police in Ferndale said the earthquake caused stucco to fall off City Hall and broke shop windows, strewing the historic downtown streets with glass shards.

"I thought a tire had blown off my truck because it was so hard to keep control of the vehicle," Officer Lindsey Frank said. "Power lines were swaying, and I could see people in the fields trying to keep their balance."

Eureka city spokesman Gary Bird said because the earthquake hit shortly before dark, only the city's old town received thorough surveys for damage. Authorities there found fallen bricks and parapets that had fallen off old structures, causing damage to adjacent buildings, he said.

"There are some frayed nerves, but I think we've come through this pretty well for the magnitude of earthquake we've had," Bird said.

Televisions tumbled and objects were knocked off walls in Arcata, a small town that's home to Humboldt State University, one resident said.

"The whole town is kind of freaked out right now," said Judd Starks, the kitchen manager at a bar and restaurant known as The Alibi. "All the power is out, people are out walking around."

The quake was felt as far south as Capitola in central California, and as far north as central Oregon, USGS geophysicist Richard Buckmaster said.

It struck about 270 miles north of San Francisco in an area where earthquakes ranging from 7.0 to 7.3 have struck periodically since the 1800s, causing damage and injuries. In 1964 a tsunami generated by a great 9.2-magnitude earthquake near Anchorage, Alaska, washed away 11 people in Crescent City, 80 miles to the north of Arcata.

There is a small chance _ 5 to 10 percent _ of another magnitude-6.5 temblor or larger hitting the area over the next week, but the odds dramatically decrease as time passes, the USGS said.

There's also a 78 percent chance of a strong and potentially damaging aftershock magnitude-5 or larger over the same period. The earthquake probabilities are based on statistical observations of past earthquakes in California and are not predictions, the USGS said.

California is one of the world's most seismically active regions. More than 300 faults crisscross the state, which sits atop two of Earth's major tectonic plates, the Pacific and North American plates. About 10,000 quakes each year rattle Southern California alone, although most of them are too small to be felt.

The damage created by an earthquake depends greatly on where it hits. A 7.1 quake _ much stronger than Saturday's 6.5 temblor _ hit the Mojave Desert in 1999 but caused only a few injuries and no deaths.

By contrast the 1994 Northridge earthquake under Los Angeles' San Fernando Valley was magnitude 6.7. It killed 72 people, injured more than 9,000 and caused $25 billion in damage in the metropolitan area. And the magnitude-7.1 quake in October 1989 struck just before the third game of the World Series at Candlestick Park. The quake, centered in the Santa Cruz Mountains on the San Andreas fault, caused nearly $3 billion in damage.

Dan Bowermaster of San Francisco was with relatives in Eureka when Saturday's quake hit, moving the refrigerator in his cousins' home about 3 feet. He said he had been in several moderate and large quakes throughout California but had never felt anything as strong as this one.

"It was extremely unsettling, it was shaking in kind of a circular way," he said.

Sandra Hall, owner of Antiques and Goodies in Eureka, said furniture fell over, nearly all her lamps broke and the handful of customers in her store got a big scare. She said it was the most dramatic quake in the 30 years the store has been open.

"We'll be having a sale on broken china for those who like to do mosaics," she said.

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Dalton reported from Los Angeles. Associated Press writers Alicia Chang in Los Angeles and Bob Christie in Phoenix contributed to this report.